1. Field of the Invention
The invention relates to a dielectric antenna having a dielectric feeding section, a first transition section comprising a dielectric rod, a dielectric emitting section, and, a further, second transition section forming a dielectric horn and, wherein the feeding section can be struck with electromagnetic radiation, electromagnetic radiation can be guided with the first transition section and the second transition section and the electromagnetic radiation can be emitted from the emitting section as airborne waves.
2. Description of Related Art
Dielectric antennae per se have been known for a long time and are used in different forms and sizes for very different purposes, as, for example, also in industrial process control for determining distances—for example of media surfaces in tanks—using running time evaluation of reflected electromagnetic waves (radar applications). The invention described here is completely independent of the field in which the following antennae are used; the application in the field of fill level measurement for the antennae being discussed here is only exemplary in the following.
In dielectric antennae known from the prior art, the emitting section and the second transition section forming a dielectric horn overlap and are normally called horn antennae—or also horn emitter in the case of emission. Such a dielectric antenna is supplied by a metallic waveguide with a TE-wave or a TM-wave, as e.g. TE11-wave (same as a H11-wave), whose electric field intensity has no share in the transmission direction of the electromagnetic wave. The electromagnetic wave guided by the waveguide transmits itself via the dielectric feeding section into the first transmission section comprising the dielectric rod and from there into the second transmission section forming a dielectric horn and is guided further to the antenna aperture of the second transmission section, which forms the emitting section in this case, and is emitted via this antenna aperture into the room as a free wave. As opposed to the widespread horn antennae having metallic walls, dielectric antennae consist essentially of a body of the dielectric material, wherein electromagnetic waves are also guided in the material and are emitted in the direction of emission via the material. “Direction of emission” is meant here essentially to be the main direction of emission of the dielectric antenna, i.e. the direction in which the directivity of the dielectric antenna is particularly pronounced.
Dielectric antennae are often used in industrial process measurement—as was mentioned in the introduction—for fill level measurement. It is of particular advantage for such applications when theses antennae have a thin as possible main direction of emission and, at the same time, a compact as possible construction. These demands, however, are contradictory in view of constructive measures that normally occur in their technical implementation.
A thin directivity in the main direction of emission can be first achieved using a large antenna aperture—thus opening surface—of the emitting section, which makes a large extension of the antenna necessary perpendicular to the main direction of emission. So that the antenna aperture is also used in the sense of a thin main direction of emission, the electromagnetic radiation emitted from the emitting section has to have an even as possible phase front, wherein such an even phase front can only, for the most part, be implemented with increasing length of the antenna, which is also contradictory to the desired compact construction. In the field of fill level measurement, an additional problem also occurs in that the geometric antenna aperture can only be enlarged within narrow bounds, since the antenna cannot be otherwise introduced in the capacity to be monitored—e.g. via already existing tank openings and spouts—and can no longer be mounted there. Furthermore, electromagnetic waves—due to the geometric conditions of the mounting situation—have to be guided through mounting geometries with low radiation in order to avoid parasitic in-tank reflection, which lead to a distortion of the wanted signal.